The university's Transportation Research Institute released results Tuesday that show the average miles per gallon that new U.S. cars get has risen steadily from just 20.1 miles in October 2007 to 24.8 miles in May 2013.

The study focused on individual models of cars, SUVs, minivans and pickup trucks, as well as the combined city and highway fuel-economy ratings established by the Environmental Protection Agency and published in its Fuel Economy Guide.